Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 157	$ 185	$ 160
Charged to Costs and Expenses	54	73	57
Deductions	(75)	(101)	(32)
Balance at End of Period	136	157	185
Deferred tax valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	178	150	286
Charged to Costs and Expenses	75	(64)	(121)
Deductions	95	92	(15)
Balance at End of Period	$ 348	$ 178	$ 150